MAX8595XETA+T - Maxim Integrated Products, Inc.

General Description

The MAX8595X/MAX8596X drive up to nine white LEDs

with constant current and high efficiency to provide

LCD backlighting in cell phones, PDAs, and other

handheld devices. The series connection allows the

LED currents to be identical for uniform brightness and

minimizes the number of traces to the LEDs. The

MAX8595X regulates constant LED current over the

entire temperature range. The MAX8596X features an

ambient-temperature derating function to avoid over-

driving the white LEDs during high ambient tempera-

tures, enabling higher drive current below +42°C.

A single Dual Mode™ input provides a simple means of

brightness adjustment and on/off control. Fast 1MHz

current-mode PWM operation allows for small input and

output capacitors and a small inductor while minimizing

ripple on the input supply/battery. Soft-start eliminates

inrush current during startup.

The MAX8595X/MAX8596X are available in a space-

saving, 8-pin, 3mm x 3mm TDFN package.

Applications

Cell Phones and Smart Phones

PDAs, Palmtops, and Wireless Handhelds

e-Books and Subnotebooks

White LED Display Backlighting

Features

♦Up to Nine LEDs at 25mA

♦Temperature Derating Function to Allow Fewer

LEDs for Same Light (MAX8596X)

♦86% Efficiency (PLEDs / PIN)

♦1.7% Current-Regulation Accuracy

♦Output Overvoltage Protection

♦Flexible Dimming Control

Analog

Direct-PWM Internal Filter

♦1MHz PWM Switching Frequency

♦0.1µF Output Capacitor

♦12mVP-P Low Input Ripple

♦Soft-Start Eliminates Inrush Current

♦2.6V to 6V Input Range

♦0.3µA Shutdown Current

♦Pin Compatible with the MAX1561 and MAX1599

♦TDFN 3mm x 3mm x 0.8mm Package with

Exposed Paddle

MAX8595X/MAX8596X

High-Efficiency, 36V Step-Up Converters

with TADerating Option for 2 to 9 White LEDs

________________________________________________________________ Maxim Integrated Products 1

GND

COMP

PGND

CTRL

OUT

TOP VIEW

MAX8595X

MAX8596X

876

TDFN

3mm x 3mm x 0.8mm

A "+" SIGN WILL REPLACE THE FIRST

PIN INDICATOR ON LEAD-FREE PACKAGES.

Pin Configuration

Ordering Information

MAX8595X

MAX8596X

IN LX

OUT

PGND

CTRL

COMP

GND

0.1µF

2 TO 9 LEDs

200Hz TO 200kHz

ANALOG OR

PWM DIMMING

2.2µF

INPUT

2.6V TO 6V

OUTPUT

UP TO 38V

Typical Operating Circuit

19-3485; Rev 2; 7/06

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

PART TEMP RANGE PIN-

PACKAGE

PKG

CODE

MAX8595XETA-T -40°C to +85°C8 TDFN-EP* T833-1

MAX8595XETA+T -40°C to +85°C 8 TDFN-EP* T833-1

MAX8596XETA-T -40°C to +85°C 8 TDFN-EP* T833-1

MAX8596XETA+T -40°C to +85°C 8 TDFN-EP* T833-1

Dual Mode is a trademark of Maxim Integrated Products, Inc.

+Denotes lead-free package. T = Tape and reel.

*EP = Exposed paddle.

MAX8595X/MAX8596X

High-Efficiency, 36V Step-Up Converters

with TADerating Option for 2 to 9 White LEDs

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional

operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to

absolute maximum rating conditions for extended periods may affect device reliability.

IN to GND .................................................................-0.3V to +7V

PGND to GND .......................................................-0.3V to +0.3V

LX, OUT to GND .....................................................-0.3V to +40V

CTRL to GND...................-0.3V to the lower of +6V or (VIN + 2V)

COMP ..........................................................-0.3V to (VIN + 0.3V)

ILX ...................................................................................1.0ARMS

ICS ........................................................25mA (VCS < VIN + 1.2V)

CS to GND ...................................................-0.3V to (VIN + 1.2V)

Continuous Power Dissipation (TA= +70°C)

8-Pin TDFN 3mm x 3mm

(derate 24.4mW/°C above +70°C)............................ 1950mW

Operating Temperature Range ...........................-40°C to +85°C

Junction Temperature......................................................+150°C

Storage Temperature Range .............................-65°C to +150°C

Lead Temperature (soldering, 10s) .................................+300°C

ELECTRICAL CHARACTERISTICS

(VIN = 3.0V, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, VCTRL = 1.5V, TA= -40°C to +85°C, unless other-

wise noted. Typical values are at TA= +25°C.) (Note 1)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Supply Voltage 2.6 6.0 V

UVLO Threshold VIN rising or falling 2.10 2.38 2.55 V

UVLO Hysteresis 30 mV

Quiescent Current No switching 0.5 0.7 mA

TA = +25°C 0.3 2

Shutdown Supply Current CTRL = GND,

VOUT = VIN TA = +85°C1

µA

OVLO Threshold VOUT rising 36 38 40 V

OVLO Hysteresis 2V

VOUT = 32V, VCTRL > 0.24V 9 20 35

TA = +25°C 0.01 1

OUT Input Bias Current OUT = IN, CTRL = GND TA = +85°C 0.1

µA

Output Voltage Range (Note 2) VIN -

VD36 V

ERROR AMPLIFIER

TA = +25°C 0.295 0.300 0.305

TA = 0°C to +85°C 0.292 0.300 0.308CTRL to CS Regulation VCTRL = 1.50V,

VIN = 2.6V to 5.5V

TA = -40°C to +85°C 0.290 0.300 0.310

TA = +25°C 0.01 1

CS Input Bias Current VCS = VCTRL / 5 TA = +85°C 0.03 µA

MAX8595X, VCTRL = 3.0V 310 330 347

TA = -40°C to +25°C 330 345 360

TA = +42°C 343

CS Maximum Brightness Clamp

Voltage MAX8596X,

VCTRL = 3.0V TA = +85°C 106.5

MAX8595Z 1.65

CTRL Voltage for CS Maximum

Brightness Clamp MAX8596Z 1.72 V

CS Derating Function Start

Temperature MAX8596Z, VCTRL = 3.0V +42 °C

MAX8595X/MAX8596X

High-Efficiency, 36V Step-Up Converters

with TADerating Option for 2 to 9 White LEDs

_______________________________________________________________________________________ 3

ELECTRICAL CHARACTERISTICS (continued)

(VIN = 3.0V, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, VCTRL = 1.5V, TA= -40°C to +85°C, unless other-

wise noted. Typical values are at TA= +25°C.) (Note 1)

PARAMETER CONDITIONS MIN TYP MAX UNITS

CS Derating Function Slope MAX8596X, VCTRL = 3.0V, TA = +42°C to +85°C -5.5 mV/°C

CTRL Input Resistance VCTRL < 1.5V 250 500 780 kΩ

CTRL Dual-Mode Threshold 100 170 240 mV

CTRL Dual-Mode Hysteresis 5mV

CTRL Shutdown Enable Delay (Note 3) 6.0 8.2 10.5 ms

CS to COMP Transconductance VCOMP = 1.5V 32 50 82 µS

COMP Input Resistance to

Ground In shutdown, UVLO or OVLO 20 kΩ

OSCILLATOR

Operating Frequency 0.75 1.0 1.25 MHz

PWM mode 12

Minimum Duty Cycle Pulse skipping 0 %

Maximum Duty Cycle CTRL = IN, CS = GND 94 95 %

n-CHANNEL SWITCH

LX On-Resistance ILX = 190mA 0.8 1.35 Ω

TA = +25°C 0.01 5

LX Leakage Current VLX = 36V, CTRL = GND TA = +85°C1

µA

LX Current Limit Duty cycle = 90% 500 700 900 mA

Note 1: Parameters are 100% production tested at TA= +25°C. Limits over the operating temperature range are regulated by

design and characterization.

Note 2: VDis the forward-voltage drop of the Schottky diode in Figure 1.

Note 3: Time from CTRL going below the Dual-Mode threshold to IC shutdown.

MAX8595X/MAX8596X

High-Efficiency, 36V Step-Up Converters

with TADerating Option for 2 to 9 White LEDs

4 _______________________________________________________________________________________

Typical Operating Characteristics

(Circuit of Figure 1, VIN = 3.6V, ILED = 25mA, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, 4 LEDs, TA= +25°C,

unless otherwise noted.)

EFFICIENCY

vs. INPUT VOLTAGE

MAX8595X toc01

INPUT VOLTAGE (V)

EFFICIENCY (%)

543

100

3 LEDs

4 LEDs

6 LEDs

8 LEDs

EFFICIENCY

vs. LED CURRENT

MAX8595X toc02

LED CURRENT (mA)

EFFICIENCY (%)

252015105

030

3 LEDs

6 LEDs

8 LEDs

LED CURRENT

vs. DIRECT-PWM DIMMING

MAX8595X toc03

DUTY CYCLE (%)

LED CURRENT (mA)

80604020

0100

LED CURRENT

vs. AMBIENT TEMPERATURE

MAX8595X toc04

TEMPERATURE (°C)

LED CURRENT (mA)

806020 400-20

-40 100

MAX8596,

ILED = 25mA AT TA = +25°C

MAX8595,

ILED = 15mA

SWITCHING WAVEFORMS

MAX8595X toc05

500ns/div

VIN 20mV/div

AC-COUPLED

200mV/div

AC-COUPLED

100mA/div

10V/div

VLX

VOUT

SOFT-START AND SHUTDOWN RESPONSE

MAX8595X toc06

20ms/div

VCTRL 2V/div

40mA/div

10V/div

100mA/div

IIN

ILED

VOUT

MAX8595X/MAX8596X

High-Efficiency, 36V Step-Up Converters

with TADerating Option for 2 to 9 White LEDs

_______________________________________________________________________________________ 5

Typical Operating Characteristics (continued)

(Circuit of Figure 1, VIN = 3.6V, ILED = 25mA, L = 22µH, CIN = 2.2µF, COUT = 0.1µF, CCOMP = 0.1µF, RSENSE = 13Ω, 4 LEDs, TA= +25°C,

unless otherwise noted.)

Pin Description

PIN NAME FUNCTION

1 OUT

Overvoltage Sense. When VOUT is greater than 38V (typ), the internal n-channel MOSFET turns off

until VOUT drops below 36V (typ), then the IC reenters soft-start. Connect a 0.1µF ceramic capacitor

from OUT to ground. In shutdown, VOUT is one diode drop below VIN.

2IN

Input Voltage Supply. The input voltage range is 2.6V to 6.0V. Connect a 2.2µF ceramic capacitor

from IN to GND.

3 CTRL

Brightness Control Input. The voltage applied to CTRL controls LED brightness. Varying the voltage

from 0.24V to 1.65V (1.72V for the MAX8596X) adjusts the brightness from dim to 100% brightness,

respectively. Any voltage above 1.65V (1.72V) does not increase brightness. Hold CTRL below

100mV to shut down the IC after an 8.2ms delay.

4CS

Current-Sense Feedback Input. Connect a resistor from CS to GND to set the LED bias current. The

voltage at CS regulates to VCTRL / 5 or 0.330V (0.343V for the MAX8596X), whichever is lower.

5 COMP

Compensation Input. Connect a 0.1µF ceramic capacitor (CCOMP) from COMP to GND. CCOMP

stabilizes the converter, controls soft-start, and lowpass filters direct PWM dimming at CTRL. CCOMP

discharges to 0V through an internal 20kΩ resistor in shutdown.

6 GND Ground. Connect to PGND and the exposed pad directly under the IC.

7 PGND Power Ground. Connect to GND and the exposed pad directly under the IC.

8LX

Inductor Connection. Connect LX to the node between the inductor and the Schottky diode. LX is

high impedance in shutdown.

—EP

Exposed Pad. Connect to a large ground plane for maximum package heat dissipation. Connect

directly to GND and PGND under the IC.

DIRECT-PWM DIMMING RESPONSE

MAX8595X toc08

10µs/div

VCTRL

2V/div

32kHz 50%

DUTY CYCLE

500mV/div

AC-COUPLED

10mA/div

20mV/div

AC-COUPLED

VIN

VOUT

ILED

CTRL STEP RESPONSE

MAX8595X toc07

20ms/div

VCTRL 1V/div

40mA/div

10V/div

100mA/div

IIN

ILED

VOUT

MAX8595X/MAX8596X

Detailed Description

The high efficiency and small size of the MAX8595X/

MAX8596X make them ideally suited to drive up to nine

series-connected LEDs. These devices operate as a

boost DC-DC converter that regulates output current

rather than voltage. The MAX8595X/MAX8596X provide

even illumination by sourcing the same output current

through each LED, eliminating the need for expensive

factory calibration. The fast 1MHz internal oscillator

allows for a small inductor and small input and output

capacitors while minimizing input and output ripple.

The single analog control input (CTRL) allows easy

adjustment of LED brightness and on/off control. This

allows simple logic-level on/off control, analog voltage

control, or PWM duty-cycle control of both brightness

and shutdown. In shutdown, supply current is reduced

to a low 0.3µA (typ). A soft-start gradually illuminates

the LEDs, eliminating the inrush current during startup.

The MAX8596X has the additional feature of derating

LED current as ambient temperature rises. Above

+42°C, the CS regulation voltage is reduced at a rate of

5.5mV/°C, thus reducing the LED current.

Soft-Start

The MAX8595X/MAX8596X attain soft-start by charging

CCOMP gradually with a current source. When VCOMP

rises above 1.25V, the internal MOSFET begins switch-

ing at a reduced duty cycle. When VCOMP rises above

2.25V, the duty cycle is at its maximum. See the

Typical Operating Characteristics for an example of

soft-start operation.

Shutdown

The MAX8595X/MAX8596X enter shutdown when VCTRL

is less than 100mV for more than 8.2ms. In shutdown,

supply current is reduced to 0.3µA (typ) by powering

down the entire IC except for the CTRL voltage-detec-

tion circuitry. CCOMP is discharged during shutdown,

allowing the device to reinitiate soft-start when it is

enabled. Although the internal n-channel MOSFET does

not switch in shutdown, there is still a DC current path

between the input and the LEDs through the inductor

and Schottky diode. The minimum forward voltage of the

LED array must exceed the maximum input voltage to

ensure that the LEDs remain off in shutdown. However,

with two or more LEDs, the forward voltage is large

enough to keep leakage current low, less than 1µA

(typ). Typical shutdown timing characteristics are shown

in the Typical Operating Characteristics.

Overvoltage Protection

Overvoltage lockout (OVLO) occurs when VOUT is

above 38V (typ). The protection circuitry stops the inter-

nal MOSFET from switching and causes VCOMP to

decay towards 0V. The device comes out of OVLO and

into soft-start when VOUT falls below 36V (typ).

Ambient Temperature Derating Function

(MAX8596X)

The MAX8596X limits the maximum LED current

depending on the die temperature. VCS is limited to

343mV up to +42°C. Once the temperature reaches

+42°C, the maximum VCS declines by 5.5mV/°C until

the minimum 106.5mV threshold is reached at +85°C.

Due to the package’s exposed paddle, the die temper-

ature is always very close to the PC board temperature.

The temperature derating function allows the LED cur-

rent to be safely set higher at normal operating temper-

atures, thereby allowing either a brighter display or

fewer LEDs to be used for normal display brightness.

See the Typical Operating Characteristics for LED

Current vs. Ambient Temperature.

High-Efficiency, 36V Step-Up Converters

with TADerating Option for 2 to 9 White LEDs

6 _______________________________________________________________________________________

0.1µF

PWM

CONTROL

2.2µF

22µH

PGND

OVER-

VOLTAGE

PROTECT

SHUTDOWN8.2ms

GND

COMP

CTRL

170mV

100kΩ

121kΩ279kΩ

1.25V CLAMP OR

TEMP DERATE CLAMP

RSENSE

13Ω

2.6V TO 6.0V

fOSC

1MHz

0.1µF

ANALOG

OR DIRECT

PWM

DIMMING

OUT

Figure 1. Functional Diagram and Typical Application Circuit

Design Procedure

Adjusting LED Current

Adjusting the output current of the MAX8595X/

MAX8596X changes the brightness of the LEDs. An

analog input (CTRL) and the sense-resistor value set

the output current. Output current is given by:

ILED = VCTRL / (5 x RSENSE)

The VCTRL voltage range for adjusting output current is

0.24V to 1.65V (or 1.72V for the MAX8596X). To set the

maximum current, calculate RSENSE when VCTRL is at

its maximum as follows:

For the MAX8595X, RSENSE = 1.65 / (5 x ILED(MAX))

For the MAX8596X, RSENSE = 1.72 / (5 x ILED(MAX))

Power dissipation in RSENSE is typically less than 10mW,

allowing the use of a small surface-mount resistor.

PWM Dimming Control

CTRL is also used as a digital input allowing LED

brightness control with a logic-level PWM signal

applied directly to CTRL. The frequency range is from

200Hz to 200kHz, while 0% duty cycle corresponds to

zero current and 100% duty cycle corresponds to full

current. The error amplifier and compensation capaci-

tor form a lowpass filter so PWM dimming results in DC

current to the LEDs without the need for any additional

RC filters; see the Typical Operating Characteristics.

Capacitor Selection

Ceramic capacitors with X5R, X7R, or better dielectric

are recommended for stable operation over the entire

operating temperature range. The exact values of input

and output capacitors are not critical. The typical value

for the input capacitor is 2.2µF, and the typical value for

the output capacitor is 0.1µF. Higher value capacitors

can be used to reduce input and output ripple, but at

the expense of size and higher cost. CCOMP stabilizes

the converter and controls soft-start. Connect a 0.1µF

capacitor from COMP to GND. For stable operation,

COUT must not exceed 10 times CCOMP.

Inductor Selection

Inductor values range from 10µH to 47µH. A 22µH

inductor optimizes the efficiency for most applications

while maintaining low 12mVP-P input ripple. With input

voltages near 5V, a larger value of inductance can be

more efficient. To prevent core saturation, ensure that

the inductor-saturation current rating exceeds the peak

inductor current for the application. Calculate the peak

inductor current with the following formula:

Schottky Diode Selection

The high switching frequency of the MAX8595X/

MAX8596X demands a high-speed rectification diode

(D1) for optimum efficiency. A Schottky diode is recom-

mended due to its fast recovery time and low forward-

voltage drop. Ensure that the diode’s average and

peak current rating exceed the average output current

and peak inductor current. In addition, the diode’s

reverse breakdown voltage must exceed VOUT. The

RMS diode current can be approximated from:

Applications Information

Compensation Information

The dominant pole (fDP) of the error amplifier is given by:

The output pole is given by

where ROUT is the sum of RSENSE and the incremental

series resistance of the white LED string.

Continuous conduction introduces a right-half-plane

zero determined by

RHPZ IN

OUT

=⎛

⎝

⎜⎞

⎠

⎟××2π

fRC

OUT OUT OUT

=××

2π

fMC

DP COMP

=×

4Ω

III

DIODE RMS OUT PEAK()

=×

IVI

PEAK OUT MAX LED MAX

IN MIN

=×

×+×

() ()

()

MAX8595X/MAX8596X

High-Efficiency, 36V Step-Up Converters

with TADerating Option for 2 to 9 White LEDs

_______________________________________________________________________________________ 7

MAX8595X/MAX8596X

In applications using large RSENSE, it may be necessary

to add a series resistor (RCOMP) to CCOMP to increase

control loop phase margin. See Figure 2 for details.

The frequency of the zero is given by:

Consult the factory for further information.

PC Board Layout

Due to fast switching waveforms and high-current

paths, careful PC board layout is required. An evalua-

tion kit (MAX8596XEVKIT) is available to speed design.

When laying out a board, minimize trace lengths

between the IC and RSENSE, the inductor, the diode,

the input capacitor, and the output capacitor. Keep

traces short, direct, and wide. Keep noisy traces, such

as the LX node trace, away from CS. The IN bypass

capacitor (CIN) should be placed as close to the IC as

possible. PGND and GND should be connected direct-

ly to the exposed paddle underneath the IC. The

ground connections of CIN and COUT should be as

close together as possible. The traces from IN to the

inductor and from the Schottky diode to the LEDs can

be longer.

Chip Information

TRANSISTOR COUNT: 2143

PROCESS: BiCMOS

fRC

ZCOMP COMP

=××

2π

High-Efficiency, 36V Step-Up Converters

with TADerating Option for 2 to 9 White LEDs

8 _______________________________________________________________________________________

GND

COMP

RCOMP

CCOMP

Figure 2. Alternative Compensation Circuit

MAX8595X/MAX8596X

High-Efficiency, 36V Step-Up Converters

with TADerating Option for 2 to 9 White LEDs

_______________________________________________________________________________________ 9

MAX8595X/MAX8596X

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

6, 8, &10L, DFN THIN.EPS

21-0137

PACKAGE OUTLINE, 6,8,10 & 14L,

TDFN, EXPOSED PAD, 3x3x0.80 mm

MAX8595X/MAX8596X

High-Efficiency, 36V Step-Up Converters

with TADerating Option for 2 to 9 White LEDs

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

10 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

Package Information (continued)

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

COMMON DIMENSIONS

SYMBOL MIN. MAX.

A 0.70 0.80

D 2.90 3.10

E 2.90 3.10

A1 0.00 0.05

L 0.20 0.40

PKG. CODE N D2 E2 eJEDEC SPEC b[(N/2)-1] x e

PACKAGE VARIATIONS

0.25 MIN.k

A2 0.20 REF.

2.30±0.101.50±0.106T633-1 0.95 BSC MO229 / WEEA 1.90 REF0.40±0.05

1.95 REF0.30±0.050.65 BSC2.30±0.108T833-1

2.00 REF0.25±0.050.50 BSC2.30±0.1010T1033-1

2.40 REF0.20±0.05- - - - 0.40 BSC1.70±0.10 2.30±0.1014T1433-1

1.50±0.10

MO229 / WEEC

MO229 / WEED-3

0.40 BSC - - - - 0.20±0.05 2.40 REFT1433-2 14 2.30±0.101.70±0.10

T633-2 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF

T833-2 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF

T833-3 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF

-DRAWING NOT TO SCALE-

21-0137

PACKAGE OUTLINE, 6,8,10 & 14L,

TDFN, EXPOSED PAD, 3x3x0.80 mm

2.30±0.10 MO229 / WEED-3 2.00 REF0.25±0.05

0.50 BSC

1.50±0.1010T1033-2

Revision History

Pages changed at Rev 2: 1, 2, 5–8